rectangular area lights had wrong coordinates (probably achievable with proper matrix but swapping and negating axis seems ok for now)

Plus a few styling enhancements.

[[Split portion of a mixed commit.]]

Fixed a type error for dimensions of rectangular area lights 

* You only have to do layout.prop if you want 1 property, no need for row then!
* Use col, row, sub as variable names, not colsub, rowsub, row2 etc please.
* Povray Addon: Still used a lot of splits, you need no split when you only have 1 column! 

- remove/comment unused variables
- remove unused imports
- fixed some bugs using incorrect variables

Added export of only renderable objects via outliner hide_render property and active layers. Also thanks to all those who helped bringing instances through their designs or advice: Conz, mont29, Campbell.

Render POVRay addon: Now using instances for objects’ data, to avoid having exported hundred times the same mesh/material…
Coded in collaboration with MauriciusRay.

Added spacing_multiplier to object photons block so per object photon count tuning is now possible (see tooltip)

Reorganized the whole pov properties, to place them in PropertyGroups, rather than cluttering the Scene/Material/etc. objects’ spaces…
Also added a new file handling the conversion from existing files using the old pov properties (call the ˘povray render: update to script v0.0.9” operator (bpy.ops.scene.pov_update_properties) in the search box of the 3d views to make the conversion).

*Refactored the whole in-render loop, was inherited from POV 3.6 version, and no more relevant for POV 3.7…

Further Error handling to allow win 32 bits blender builds to render with Povray 64 bits and the other way around.

pep8 edits for povray, also dont use string addition for textblock contents, write newlines separate.

* More Code cleanup, please watch and learn. :) 

* Code cleaunp

Notes:
*Why do we have some empty panels with no actual content?
*Why is split used when there is only 1 column?

The Povray script has always been some kind of example for other exporters, the UI code need some more cleanup for sure!

zero length bones had their tail offset in the wrong direction.